In recent years surgical implants, e.g. for hip replacement operations, have become more routinely fitted. Current research in the design of hip replacement joints has suggested the desirability of accurate matching of the implant to the internal shape of the bone canal. Conventional practice for cutting and shaping bone canals, preparatory to introduction of a surgical implant, involves use of surgical cutting instruments consisting essentially of a variety of hand-held power drills, saws. reamers and cutters. Satisfactory use of such instruments requires a high degree of manual skill to cut and shape bone canals accurately. A particular difficulty arises where there is a requirement to cut or shape a tapered or curved surface, for example, to shape a bone canal for reception of the stem of a hip implant.